This error indicates there's something funny about your program files. For example, if the mixcraft8.exe file got infected with a virus, you'd get this error. Or maybe if you had some program files from one build mixed with program files from another.

Re-installing is the way to fix it, but then the question would be why would the problem crop up again?

1. Does it happen again if you don't modify any Mixcraft files?
2. If it does, you should maybe do a deep virus scan.